The invention pertains to pneumatically powered percussion tools of a type designed to be held in pressed relation to the work under pressure exerted by the operator on the handle of the tool.
In tools of this nature, a piston hammer is pneumatically reciprocated at a rapid rate to pound a work implement. The force of the blows transmitted to the work varies with the pressure exerted by the operator upon the handle of the tool. A problem with existing tools of this general nature arises from the shock and vibration accompanying such operation which is transmitted to the operator through the handle. This subjects the operator to undesirable discomfort and is alleged to impair blood circulation in the hand, allegedly damaging the capillary vessels. This condition is commonly referred to as "white hand" or "chipper's syndrome."
One attempt at solving the aforementioned problem is disclosed in U.S. Pat. No. 3,727,700, invented by Lester A. Amtsberg, and issued Apr. 17, 1973.
Another example, shown in U.S. Pat. No. 2,019,964, issued Nov. 5, 1935 to F. B. Hamerly, provides limited vibration dampening through compression of one of a pair of axially opposed cushion members internally disposed within the tool. The radial restraint imposed by such an arrangement limits radial deformation and consequent dampening capability of the cushion members. Also, even though an oil resistant resilient liner extends through one of the members, adequate sealing is not provided to protect the member from the deleterious effects of oil carried in compressed air passing therethrough.
U.S. Pat. No. 2,058,583, issued Oct. 27, 1936 to F. P. Forss, attempts to overcome the above-described limitations of the Hamerly arrangement. In the Forss patent, complete isolation of the handle from vibration is prevented by a pressurized fluid conducting rigid metal sleeve which protects the cushion member from damage by lubricants carried in the pressurized fluid. An upper end of the metal sleeve is pressed into the handle while the opposite lower end, disposed in close proximity to the vibration producing elements, slidably engages a metal ring secured to the cushion member. Compression of the cushion member is limited to the amount of clearance provided between the lower end of the rigid sleeve and the vibration producing elements. Thus the ability of the cushion member to absorb vibrational forces acting in a direction toward the handle is restricted. The capability of the metal sleeve to protect the cushion member from contamination by lubricants is solely dependent on the integrity of the metal-to-metal sliding joint between the sleeve and ring. Such joints are generally undesirable for sealing since some clearance between the contacting surfaces must be provided to permit free and substantially frictionless movement therebetween. It is normal for initially controlled tolerances to increase during operation, thereby decreasing the sealing ability of the joint. Additionally, while the rigid sleeve does not inhibit stretching or extension of the cushion member in absorbing vibrational forces acting in a direction away from the handle, such extension draws the lower end of the sleeve away from the vibration producing elements, simultaneously decreasing the sealing surface contact area between the sleeve and ring. The reduced sealing surface contact area further reduces the sealing ability of the joint.
Another structure is shown in U.S. Pat. No. 2,035,643, issued Mar. 31, 1936 to C. N. Douglass et al. The shortcomings of this prior art structure are similar to those of the above-described Forss patent.
It is desirable to provide a pneumatic percussion tool with a handle which is isolated from vibrations, and which overcomes the shortcomings of the prior art.